Golf ball and manufacturing method thereof

ABSTRACT

A golf ball of one aspect of the present invention includes a spherical core, one or more cover members to cover the core, and a coating layer to coat a cover member configuring an outermost layer of the one or more cover members. A plurality of dimples is formed in the cover member of the outermost layer. Roughness is produced on a surface of the coating layer after applying a coat over the cover member of the outermost layer. An average value Fa (mm) of maximum depths of the plurality of dimples and arithmetic average roughness Ra (μm) on the surface of the coating layer, satisfy a relational expression:
 
−1.5× Fa +0.8 ≦Ra ≦−1.5× Fa +1.8.

CROSS REFERENCE

This application claims priority to Japanese Patent Application No.2014-266182 filed on Dec. 26, 2014, which is hereby incorporated byreference in its entirety.

FIELD

The present invention pertains to a golf ball and a manufacturing methodthereof.

BACKGROUND

The golf ball has a multiplicity of dimples on its surface. The dimplescauses turbulence of air flows around the golf ball when flying, therebycreating a turbulent separated flow. This phenomenon is referred to as“creation of turbulence”, and this creation of turbulence shiftsbackward an air separation point from the golf ball, resulting inreducing drag (force acting in a direction of repulsion against a flyingdirection). The creation of turbulence increasingly enlarges a deviationbetween an upper air separation point and a lower air separation pointof the golf ball due to a backspin, thereby augmenting a dynamic liftacting on the golf ball. Accordingly, well-designed dimples createbetter turbulence of the air flows and produce a longer carry.

In recent years, a technology has been also developed to enhanceaerodynamic characteristics by polishing the surface of the golf ball inaddition to contriving a shape of a dimple. For instance, JapanesePatent Application Laid-Open Publication No. 2004-14783 proposes amethod for applying a blast treatment over the surface of a coatinglayer in order to reduce the drag when the golf ball flies. Anotherinstance is that Japanese Patent Application Laid-Open Publication No.2007-260317 proposes a method for applying a rough surface work to abottom surface of the dimple in order to reduce the drag and improve thedynamic lift when the golf ball flies. Still another instance is thatJapanese Patent Application Laid-Open Publication No. 2002-369896proposes a method for forming micro dimples each having a diameter equalto or smaller than ½ as small as a diameter of the dimple formed by theblast treatment in order to extend the carry of the golf ball. Yetanother instance is that Japanese Translation of PCT InternationalApplication Publication No. 2014-520654 proposes a method for providingroughness to the surface by polishing the surface of the golf ball inorder to have an influence on aerodynamic performance of the golf ball.

A long carry is demanded of a driver shot, and, however, when an extradynamic lift is caused by the influence of the dimples, a flying golfball has a hopping trajectory, resulting a possibility that the carryshortens. Although a variety of examinations have hitherto been made notto generate the hopping trajectory in designing the dimples, thisproblem still remains unsolved, and it is desirable to develop a methodfor improving the aerodynamic performance of the golf ball not confinedto the design of the dimple.

SUMMARY

There has been also developed a technology of enhancing the aerodynamicperformance of the golf ball by producing the roughness on the surfaceof the golf ball. However, a process of producing the roughness on thesurface of the golf ball and the design of the dimples has been examinedseparately and independently. In other words, the dimple and the surfaceroughness are given as two factors for influencing the aerodynamicperformance of the golf ball, and, however, no examination about acorrelation between these two factors has been made so far. Inventors ofthe present invention found out this point and reached an idea of havinga feasibility of improving the carry of a hitting ball of the drivershot by attaining decreases in drag and in dynamic lift of the flyinggolf ball owing to the correlation between the dimple and the surfaceroughness.

A golf ball according to one aspect of the present invention includes aspherical core, one or more cover members to cover the core, and acoating layer to coat a cover member configuring an outermost layer ofthe one or more cover members. A plurality of dimples is formed in thecover member of the outermost layer, roughness is produced on a surfaceof the coating layer after applying a coat over the cover member of theoutermost layer, and an average value Fa (mm) of maximum depths of theplurality of dimples and arithmetic average roughness Ra (μm) on thesurface of the coating layer, satisfy a relational expression given infollowing Mathematical Expression 1.−1.5×Fa+0.8≦Ra≦−1.5×Fa+1.8.  [Mathematical Expression 1]Note that a unit of “Fa” in the relational expression of MathematicalExpression 1 is “mm” (millimeter), and a unit of “Ra” is “μm”(micrometer). Only values of Fa and Ra are substituted into MathematicalExpression 1 without taking account of these units.

According to the configuration described above, the relationalexpression given in Mathematical Expression 1 specifies the correlationbetween the depth of the dimple and the surface roughness of the coatinglayer. As demonstrated in Examples that will be described later on, theinventors of the present invention found out that the carry of the driveshot was improved when the depth of the dimple and the surface roughnessof the coating layer had the correlation given in MathematicalExpression 1. In other words, the configuration described above enablesthe flying performance of the golf ball to be enhanced owing to amultiplier effect of the depth of the dimple and the surface roughnessof the coating layer.

In the golf ball according to one aspect, the arithmetic averageroughness Ra on the surface of the coating layer may be equal to orlarger than 0.4 μm.

In the golf ball according to one aspect, the roughness on the surfaceof the coating layer may be acquired by a surface treatment of sprayingfine particles over the surface.

A method for manufacturing a golf ball according to another aspect ofthe present invention includes: a step of forming a spherical core; astep of covering the core with one or more cover members, and forming aplurality of dimples in a cover member configuring an outermost layer ofthe one or more cover members; a step of coating the cover member of theoutermost layer with a coating layer; and a step of producing roughnesson a surface of the coating layer, and an average value Fa (mm) ofmaximum depths of the plurality of dimples to be formed and arithmeticaverage roughness Ra (μm) on the surface of the coating layer, satisfy arelational expression given in Mathematical Expression 1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view with some portions being cut off,schematically illustrating a golf ball according to an embodiment.

FIG. 2 is a partially enlarged sectional view schematically depictingthe golf ball according to the embodiment.

FIG. 3 is a front view of the golf ball 1 according to the embodiment.

FIG. 4 is a plan view of the golf ball according to the embodiment.

FIG. 5 is a view schematically illustrating a method for producingroughness by use of an airgun.

FIG. 6 is a graph depicting a relation between an average maximum heightFa of the dimples and arithmetic average roughness Ra of the coatinglayer of the golf ball according to the Examples and ComparativeExamples.

DESCRIPTION OF EMBODIMENT

An embodiment (which will hereinafter be also termed the presentembodiment) according to one aspect of the present invention, will bedescribed based on the drawings. However, the present embodiment, whichwill be discussed below, is merely an exemplification of the presentinvention in every respect. A variety of improvements and modificationsmay be made without deviating from the scope of the present invention.In other words, a specific configuration corresponding to the embodimentmay be properly adopted upon carrying out the present invention. Notethat the description will be made based on directions on planes of thedrawings for the convenience of explanation in the following discussion.

§1 Example of Configuration

[Golf Ball]

A golf ball 10 according to the present embodiment will be describedwith reference to FIGS. 1 and 2. FIG. 1 is a sectional view with someportions being cut off, schematically illustrating the golf ball 10according to the present embodiment. FIG. 2 is a partially enlargedsectional view schematically depicting the golf ball 10 according to theembodiment.

As illustrated in FIG. 1, the golf ball 10 according to the embodimentincludes a spherical core 1, an intermediate layer 2 covering the core1, a cover 3 covering the intermediate layer 2, a plurality of dimples 5formed over the surface of the cover 3, and a coating layer 4 coatedover the surface of the cover 3. These components will hereinafter bedescribed.

Note that a diameter of the golf ball 10, though properly settable, ispreferably 40 mm to 45 mm, and further preferably 42.67 mm or larger interms of satisfying standards of United States Golf Association (USGA).It is also preferable in terms of restraining air resistance that thediameter of the golf ball 10 is set equal to or smaller than 44 mm andmore preferably equal to or smaller than 42.80 mm. It is preferable thata mass of the golf ball 10 is equal to or larger than 40 g and equal tosmaller than 50 g. Especially in terms of obtaining a large inertia, themass of the golf ball 10 is, preferably, equal to or larger than 44 gand further preferably equal to or larger than 45.00 g. In terms ofsatisfying the standards of USGA, it is preferable that the mass of thegolf ball 10 is equal to or smaller than 45.93 g.

<Core>

The description starts with the core 1. The core 1 is configured bycrosslinking rubber compositions. A material of the core 1 may besuitably selected, and a base rubber of the rubber composition of thecore 1 is exemplified by polybutadiene, polyisoprene, styrene-butadienecopolymer, ethylene-propylene-diene copolymer, and a natural rubber. Twoor more types of rubbers may be used in combination as the material ofthe core 1. The material of the core 1 is preferably polybutadiene and,more preferably, high cis-polybutadiene in particular in terms ofperformance of repulsion.

The rubber composition of the core 1 contains a co-cross-linking agent.The co-cross-linking agents being preferable in terms of the performanceof repulsion are zinc acrylate, magnesium acrylate, zinc methacrylateand magnesium methacrylate. It is preferable that the rubber compositioncontains organic peroxide together with the co-cross-linking agent. Thepreferable organic peroxide is exemplified by dicumyl peroxide,1,1-bis(t-butyl peroxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butyl peroxy) hexane, and di-t-butyl peroxide.

The rubber composition of the core 1 may contain additive agentsinstanced by a filler, sulphur, a vulcanization accelerator, a sulphurcompound, an antioxidant, a coloring agent, a plasticizing agent, adispersant, carboxylic carboxylate and other equivalent additive agents.The rubber composition of the core 1 may further contain synthetic resinpowder or cross-linked rubber powder.

The diameter of the core 1, though properly settable, is preferablyequal to or larger than 30.0 mm, and more preferably equal to or largerthan 38.0 mm. On the other hand, the diameter of the core 1 ispreferably equal to or smaller than 42.0 mm and more preferably equal toor smaller than 41.5 mm. The core 1 may have two or more layers. A shapeof the core 1 is not limited to a particular shape if spherical on thewhole, and the core 1 may have ribs on the surface. The core 1 accordingto the present embodiment is solid, and may also be hollowed.

Note that a compressive deformation quantity of the core 1 may beproperly set. However, when the compressive deformation is by farsmaller than the general standard, a ball hit feeling possibly becomesharder. Therefore, the compressive deformation quantity of the core 1 ispreferably equal to or larger than 2 mm and more preferably equal to orlarger than 2.5 mm from this point of view. Whereas when the compressivedeformation quantity of the core 1 is by far larger than the generalstandard, a ball speed upon hitting is decelerated in terms of theperformance of repulsion, resulting in a possibility that flyingperformance becomes deteriorated. Therefore, from this point of view,the compressive deformation quantity of the core 1 is preferably equalto or smaller than 6 mm and more preferably equal to or smaller than 5.5mm. The compressive deformation quantity can be measured by an optionalmethod.

<Intermediate Layer>

Next, the intermediate layer 2 will be described. The intermediate layer2 is composed of a resin composition. Although a material of theintermediate layer 2 can be suitably selected, a preferable base polymerof the resin composition of the intermediate layer 2 is an ionomerresin. The preferable ionomer resin can be exemplified by binarycopolymer of α-olefin and α,β-unsaturated carboxylic acid with a carbonnumber being “3” or above and “8” or under. Another preferable ionomerresin can be exemplified by ternary copolymer of α-olefin,α,β-unsaturated carboxylic acid with the carbon number being “3” orabove and “8” or under, and α,β-unsaturated carboxylic ester with thecarbon number being “2” or above and “22” or under. In the binarycopolymer and the ternary copolymer, the preferable α-olefin is ethyleneor propylene, and the preferable α,β-unsaturated carboxylic acid isacrylic acid or methacrylic acid. In the binary copolymer and theternary copolymer, a part of carboxyl group is neutralized with metalions. The metal ions for neutralization are exemplified by a natriumion, a potassium ion, a lithium ion, a zinc ion, a calcium ion, amagnesium ion, an aluminum ion and a neodymium ion.

The resin composition of the intermediate layer 2 may contain anotherpolymer in place of the ionomer resin. Another polymer is exemplified bypolystyrene, polyamide, polyester, polyolefin and polyurethane. Theresin composition of the intermediate layer 2 may contain two or moretypes of polymers.

The resin composition of the intermediate layer 2 may contain thecoloring agent instanced by titanium dioxide, the filler instanced bybarium sulfate, the dispersant, an antioxidant, an ultraviolet absorber,a light stabilizer, a fluorescent agent, fluorescent brightener, andother equivalent agents. Further, the resin composition of theintermediate layer 2 may contain powders of high density metalsinstanced by tungsten, molybdenum and other equivalent metals for thepurpose of adjusting a relative density.

A thickness of the intermediate layer 2, though properly settable, ispreferably equal to or larger than 0.2 mm and more preferably equal toor larger than 0.3 mm. On the other hand, the thickness of theintermediate layer 2 is preferably equal to or smaller than 2.5 mm andmore preferably equal to or smaller than 2.2 mm. The relative density ofthe intermediate layer 2 is preferably equal to or larger than 0.90 andmore preferably equal to or larger than 0.95. The relative density ofthe intermediate layer 2 is preferably equal to or smaller than 1.10 andmore preferably equal to or smaller than 1.05. The intermediate layer 2may have two or more layers. For instance, a reinforcing layer can bedisposed outside the intermediate layer 2.

Hardness of the intermediate layer 2 can be properly set. However, whenthe intermediate layer 2 is by far softer than the general standard,there exists a possibility of not adjusting a spin quantity caused whenhitting the ball by a driver or a middle iron in terms of being tough onthe outside but soft at the heart of the ball structure. Therefore, thehardness, i.e., Shore-D hardness, of the intermediate layer 2 ispreferably equal to or larger than 30 and more preferably equal to orlarger than 35 from this point of view. Whereas when the intermediatelayer 2 is by far harder than the general standard, there is likelihoodthat the ball hitting feeling becomes harder. From this point of view,the Shore-D hardness of the intermediate layer 2 is preferably equal toor smaller than 75 and more preferably equal to or smaller than 70. Notethat the Shore-D hardness can be measured by, e.g., a method thatfollows. A sheet having a thickness of approximately 2 mm ismanufactured based on injection molding by using the resin compositionsconfiguring the intermediate layer 2 and other equivalent components,and is preserved for 2 weeks at 23° C. Three or more sheets are stackednot to cause influence of a measurement substrate, in which state theShore-D hardness is measured by an automatic rubber hardness meter P1type manufactured by Kobunshi Keiki Co., Ltd., the mete P1 type beingequipped with a spring hardness meter Shore-D type specified inASTM-D2240 (American Society for Testing and Materials D2240). TheShore-D hardness of the intermediate layer 2 and other equivalentcomponents can be thus measured.

<Cover>

Next, the cover 3 will be described. The cover 3 is composed of theresin composition. Though a material of the cover 3 can be suitablyselected, a preferable base polymer of the resin composition of thecover 3 is polyurethane. The resin composition of the cover 3 maycontain thermoplastic polyurethane and may also contain thermosettingpolyurethane. The resin composition of the cover 3 is the thermoplasticpolyurethane that is preferable in terms of productivity. Thethermoplastic polyurethane contains a polyurethane component as a hardsegment, and a polyester component or a polyether component as a softsegment.

A curing agent of the polyurethane component is exemplified by alicyclicdiisocyanate, aromatic diisocyanate, and aliphatic diisocyanate.Particularly, the preferable curing agent is the alicyclic diisocyanate.The alicyclic diisocyanate has none of double bond in a main chain, andhence yellow discoloration of the cover 3 is restrained. The alicyclicdiisocyanate is exemplified by 4,4,-dicyclohexyl methane diisocyanate(H12MDI), 1,3-bis(isocyanatomethyl) cyclohexane (H6XDI), isophoronediisocynate (IPDI), and trans-1,4-cycloxane diisocyanate (CHDI). TheH12MDI is preferable in terms of general purpose properties andworkability.

The resin composition of the cover 3 may contain another polymer inplace of polyurethane. Another polymer is exemplified by the ionomerresin, polyethylene, polyamide, polyester and polyolefin. The resincomposition of the cover 3 may contain two or more types of polymers.Further, the resin composition of the cover 3 may also contain thecoloring agent instanced by titanium dioxide, the filler instanced bybarium sulfate, the dispersant, the antioxidant, the ultravioletabsorber, the light stabilizer, the fluorescent agent, the fluorescentbrightener, and other equivalent agents.

A thickness of the cover 3, though properly settable, is preferablyequal to or larger than 0.2 mm and more preferably equal to or largerthan 0.3 mm. The thickness of the cover 3 is preferably equal to orsmaller than 2.5 mm and more preferably equal to or smaller than 2.2 mm.The relative density of the cover 3 is preferably equal to or largerthan 0.90 and more preferably equal to or larger than 0.95. The relativedensity of the cover 3 is preferably equal to or smaller than 1.10 andmore preferably equal to or smaller than 1.05. Note that the cover 3 mayhave two or more layers.

The hardness of the cover 3 can be properly set corresponding to theembodiment without being limited in particular. It is, however,preferable to set the hardness of the cover 3 in terms of adjusting thespin quantity in a driver shot and an approach shot so that the Shore-Dhardness is equal to or larger than 30. The Shore-D hardness of thecover 3 is preferably equal to or larger than 32 and more preferablyequal to or larger than 34. On the other hand, the Shore-D hardness ofthe cover 3 is preferably equal to or smaller than 70 in terms of aplayer's ball hit feeling. When the hardness of the cover 3 is largerthan this level, there arises a possibility of causing a decline of theplayer's ball hit feeling such as not feeling a solid touch of the golfball 10 on the face, not feeling a firm catch, not feeling a stickycontact and not feeling an effective spin. The Shore-D hardness of thecover 3 is preferably equal to or smaller than 69 and more preferablyequal to or smaller than 68. The Shore-D hardness of the cover 3 can bemeasured by the same method for the intermediate layer 2.

Note that each of the intermediate layer 2 and the cover 3 correspondsto a “cover member” according to the present invention. The cover 3corresponds to a “cover member configuring an outermost layer” accordingto the present invention.

<Dimple>

Next, the dimples 5 will be described further with reference to FIGS. 3and 4. FIG. 3 is a front view of the golf ball 10. FIG. 4 is a plan viewof the golf ball according to the embodiment. As illustrated in FIGS. 1to 4, a plurality of dimples 5 is formed over the surface of the cover3. As depicted in FIG. 2, the dimple 5 is a recessed in concave from thesurface of an imaginary ball, and takes a circular arc shape in section.

As illustrated in FIGS. 3 and 4, the dimple 5 according to the presentembodiment is formed in the circular shape as viewed on the plane. Adiameter Dm of the dimple 5 formed in the circular shape can beindicated by a distance between both end portions of the dimple 5, towhich a straight line Tg is tangent, when depicting the straight line Tgalong the dimple 5 as illustrated in FIG. 2. The diameter Dm of thedimple 5, though properly settable, is set preferably within a range of2.0 mm to 6.0 mm. The dimples 5 with the diameter Dm being equal to orlarger than 2.0 mm contributes to the creation of turbulence of the golfball 10. From this point of view, the diameter Dm of the dimple 5 ismore preferably equal to or larger than 2.2 mm and much more preferablyequal to or larger than 2.4 mm. While on the other hand, when thediameter Dm of the dimple 5 exceeds 6.0 mm, an external appearance ofthe spherical golf ball 10 is spoiled. From this point of view, thediameter Dm of the dimple 5 is more preferably equal to or smaller than5.8 mm and much more preferably equal to or smaller than 5.6 mm.

A curved line 11 (one-dotted chain line) in FIG. 2 represents thesurface of the golf ball 10 (which will hereinafter be referred to asthe “imaginary ball”) on the assumption that the dimple 5 does notexist. Therefore, a maximum depth Dp of the dimple 5 can be, asillustrated in FIG. 2, indicated by a distance between the surface(curved line 11) of the imaginary ball and a deepest portion of thedimple 5. Such a maximum depth Dp of the dimple 5, though properlysettable, is preferably equal to or larger than 0.10 mm, more preferablyequal to or larger than 0.13 mm, and much more preferably equal to orlarger than 0.15 mm in terms of restraining the golf ball 10 fromhopping during the flight. On the other hand, the maximum depth Dp ofthe dimple 5 is preferably equal to or smaller than 0.65 mm, morepreferably equal to or smaller than 0.55 mm, and much more preferablyequal to or smaller than 0.40 mm in terms of restraining the golf ball10 from dropping during the flight.

Note that an average value Fa (mm) of the maximum depths Dp of thedimples 5 can be calculated by dividing a total of the maximum depths Dpof all of the dimples 5 by a number of dimples 5. This average value Fa(mm) may be utilized as an index for representing a shape of each dimple5. The average value Fa (mm) can be properly set to satisfy a relationalexpression given in Mathematical Expression 1 described above. However,when the average value Fa (mm) is by far smaller than the generalstandard, a flight line of the ball appears to hop, resulting in anincreased possibility of the carry being ill-affected. Whereas when theaverage value Fa (mm) is by far larger than the general standard, theflight line of the ball is lowered, resulting in the increasedpossibility of the carry being ill-affected. From this point of view,the average value Fa (mm) of the maximum depths of the dimples 5 is setpreferably within a range of 0.18 mm to 0.33 mm, more preferably withina range of 0.20 mm to 0.32 mm, and much more preferably within a rangeof 0.22 mm to 0.31 mm.

Herein, a portion surrounded by the surface (curved line 11) of theimaginary ball and the surface of the dimple 5 can be grasped as avolume of the dimple 5. A total volume of the dimples 5 can becalculated by adding the volumes of all of the dimples 5. The totalvolume of the dimples 5, though properly settable, is preferably equalto or larger than 450=³, more preferably equal to or larger than 480mm³, and much more preferably equal to or larger than 500 mm³ in termsof restraining the golf ball 10 from hopping during the flight. While onthe other hand, the total volume of the dimples 5 is preferably equal toor smaller than 750 mm³, more preferably equal to or smaller than 730mm³, and much more preferably equal to or smaller than 710 mm³ in termsof restraining the golf ball 10 from dropping during the flight.

An area size of the dimple 5 can be obtained from an area circumscribedby a borderline of the dimple 5. In other words, the area size of thedimple 5 can be defined by an area size of the area circumscribed by anedge line when a center of the golf ball is viewed from infinity. Atotal area size of the dimples 5 can be calculated by adding the areasizes of all of the dimples 5. A ratio, at which the total area size ofthe dimples 5 occupies a surface area size of the imaginary ball, isreferred to as a surface area occupancy.

The surface area occupancy of the dimples 5, though properly settable,is set preferably within a range of 70% to 95%. When the surface areaoccupancy of the dimples 5 is smaller than 70%, the dynamic lift of thegolf ball 10 during the flight is likely to become deficient. From thispoint of view, the surface area occupancy of the dimples 5 is morepreferably 72% or larger, and much more preferably 75% or larger. On theother hand, when the surface area occupancy of the dimples 5 exceeds95%, there exists an increased possibility that the golf ball 10 hopsduring the flight. From this point of view, the surface area occupancyof the dimples 5 is more preferably 93% or smaller, and much morepreferably 91% or smaller.

A total number of dimples 5, though properly settable, is set preferablywithin a range of 200 to 500. When the total number of dimples 5 issmaller than 200, the surface area occupancy described above isdifficult to be attained, resulting in a likelihood that an effect ofimproving flight characteristics of the golf ball 10 is hard to beacquired. From this point of view, the total number of dimples 5 ispreferably equal to or larger than 230, and more preferably equal to orlarger than 260. Whereas when the total number of dimples 5 exceeds 500,the area size of each individual dimple 5 diminishes, which leads to alikelihood that the dimple 5 is hard to contribute to the creation ofturbulence. From this point of view, the total number of the dimples 5is more preferably equal to or smaller than 470 and much more preferablyequal to or smaller than 440.

Note that each dimple 5 is formed in the circular shape as viewed on theplane in FIGS. 3 and 4. However, the shape of the dimple 5 may not becircular but may be appropriately formed corresponding to theembodiment. All of the dimples 5 may take the same shape, and thedimples 5 taking different shapes from those of other dimples 5 maycoexist. For instance, as depicted in FIGS. 3 and 4, plural types ofdimples 5 having different diameters Dm may exist in mixture. And, thedimples 5 having different shapes may exist in mixture. An arrangementof the dimples 5 may be appropriately determined corresponding to theembodiment.

<Coating Layer>

Next, the coating layer 4 will be described. As illustrated in FIGS. 1and 2, the coating layer 4 is formed by applying a coating material overthe surface of the cover 3, and is configured to coat the cover 3. Thecoating material for forming the coating layer 4 may be suitablyselected corresponding to the embodiment. For instance, this type ofcoating material may involve using a clear coating material containingtwo-part curing type polyurethane as the base.

A thickness of the coating layer 4, though properly settable, ispreferably equal to or larger than 5.0 μm, more preferably equal to orlarger than 5.5 μm, and much more preferably equal to or larger than 6.0μm. This is because of there being a possibility that the coating layer4 exfoliates from the cover 3 in the process of forming roughness thatwill be described later on when the thickness of the coating layer 4 issmaller than 5.0 μm. On the other hand, when the thickness of thecoating layer 4, though an upper limit of the thickness is notparticularly restricted, augments, a quantity of the coating material tobe applied increases, resulting in difficulty to uniform the thicknessof the coating layer 4 over than whole golf ball 10. From this point ofview, the thickness of the coating layer 4 is preferably equal to orsmaller than 30 μm.

Hardness of the coating layer 4, though properly settable, is preferablyset so that a 10% modulus of the coating layer 4 is equal to or smallerthan 160 kgf/cm². When the 10% modulus of the coating layer 4 is large,the approach shot has a possibility of decreasing the spin quantity ofthe golf ball 10. From this point of view, the 10% modulus of thecoating layer 4 is more preferably equal to or smaller than 150 kgf/cm²and much more preferably equal to or smaller than 140 kgf/cm². On theother hand, though a lower limit of the 10% modulus of the coating layer4 is not particularly restricted, when the 10% modulus of the coatinglayer 4 is by far smaller than the general standard, tack feelingremains on the surface of the golf ball 10 because the coating layer 4is by far softer than the general standard, and the hit feeling of thegolf ball 10 has a likelihood of declining. From this point of view, the10% modulus of the coating layer 4 is preferably equal to or larger than5 kgf/cm² and more preferably equal to or larger than 10 kgf/cm². Notethat the modulus represents a stress generated when giving a fixeddistortion to the member, and the 10% modulus represents a stressgenerated when giving a 10% distortion. The 10% modulus can be measuredpursuant to the standards of JIS-K7161.

The surface of the coating layer 4 is roughed by a process that will bedescribed later on. For instance, as depicted in FIG. 2, rugged portions(concave and convex portions) not reaching the cover 3 are formed on thecoating layer 4. The roughness of the surface of the coating layer 4 canbe defined by a variety of methods, and, however, the inventors of thepresent invention defined the roughness by using arithmetic averageroughness Ra (μm). The inventors of the present invention also defined astate of the dimple 5 by using the average value Fa (mm) of the maximumdepths.

The inventors of the present invention found out that the carry of thegolf ball 10 increases, as will be demonstrated by working examplesdescribed later on, when the arithmetic average roughness Ra (μm) of thecoating layer 4 and the average value Fa (mm) of the maximum depths ofthe dimples 5 satisfy the relational expression given in MathematicalExpression 1. To be specific, the present invention enables enhancementof the flight performance of the golf ball 10 owing to a multipliereffect of the dimples 5 and the roughness produced on the surface of thecoating layer 4 by configuring the dimples 5 and the roughness of thesurface of the coating layer 4 to satisfy the relational expressiongiven in Mathematical Expression 1.

Note that the arithmetic average roughness Ra of the coating layer 4 canbe properly set to satisfy the relational expression given inMathematical Expression 1, and, however, when the roughness produced onthe surface of the coating layer 4 is by far smaller than the generalstandard, there is a likelihood that an effect of the roughness is notsufficiently exhibited. Therefore, the arithmetic average roughness Raof the coating layer 4 is preferably equal to or larger than 0.4 μm,more preferably equal to or larger than 0.45 μm, and much morepreferably equal to or larger than 0.50 μm. On the other hand, though anupper limit of the arithmetic average roughness Ra is not particularlyrestricted, when the roughness of the coating layer 4 is by far largerthan the general standard, the golf ball 10 does not acquire a neatappearance, and there is likelihood of deteriorating durability of thecoating layer 4 due to a failure of adhesion of the coating layer 4 tothe cover 3, exfoliation of the coating layer 4 from the cover 3, andother equivalent phenomena. From this point of view, the arithmeticaverage roughness Ra of the coating layer 4 is preferably equal to orsmaller than 1.50 μm. Note that the arithmetic average roughness Ra ofthe coating layer 4 can be measured pursuant to the standards of JISB0601.

§2 Manufacturing Method

Next, a manufacturing method of the golf ball 10 will be described.Specifically, the manufacturing method of the golf ball 10 can beseparated into a manufacturing process of the golf ball 10 and a processof producing the roughness on the surface of the coating layer 4 of themanufactured golf ball 10. The respective processes will hereinafter bedescribed.

[Manufacturing Process of Golf Ball]

The description starts with the manufacturing process of the golf ball10. The golf ball 10 can be manufactured by a known method. Forinstance, the golf ball 10 is manufactured as follows.

The spherical core 1 is molded by using a mold and other equivalenttools, and the intermediate layer 2 and the cover 3 are molded in thissequence around the core 1. The dimples 5 are molded concurrently withmolding the cover 3. To be specific, a plurality of protruded portionsfor molding the dimples 5 is formed over a cavity of the mold formolding the cover 3.

Subsequently, the coating material is applied over the surface of thecover 3. The coating layer 4 is formed by drying this coating material.A coating method in the case of using a curing coating material is notparticularly limited, and known methods may be adopted. By way of oneinstance, the coating method can be exemplified by spray coating,electrostatic coating and other equivalent coating methods.

In the spray coating using an air gun, a polyol component and apolyisocyanate component are supplied respectively by pumps andconsecutively mixed by a line mixer disposed just anterior to the airgun, and a obtained mixture may be spray-coated, and polyol andpolyisocyanate may also be separately coated by use of an air spraysystem equipped with a mixture ratio control mechanism. The coat may beconducted by one spray-coating process, and several layers of coat mayalso be applied a plural number of times.

The curing coating material applied over the golf ball 10 is dried at atemperature of, e.g., 30° C. to 70° C. for 1 to 24 hours, therebyenabling the coating layer 4 (coating film) to be formed.

[Process of Producing Roughness on Coating Layer]

Given next is a description of a process of producing the roughness onthe surface of the coating layer 4 of the manufactured golf ball 10. Avariety of methods of producing the roughness on the surface of thecoating layer 4 exist, and can be properly selected corresponding to theembodiment. For instance, there are two methods that will be describedbelow.

<Production of Roughness by Spraying Fine Particles>

A method of producing the roughness by spraying fine particles will bedescribed with reference to FIG. 5. FIG. 5 schematically illustrates themethod of producing the roughness by spraying the fine particles. Asdepicted in FIG. 5, the roughness can be produced on the surface of thecoating layer 4 by spraying the fine particles over the surface of thecoating layer 4.

Specifically, an apparatus depicted in FIG. 5 includes a rotary body 21serving as a seating, a plurality of support members 22 that areconnected to the rotary body 21 and configured to support the golf ball10, and an air gun 23 for spraying the fine particles over the supportedgolf ball 10. After the manufacturing process described above, the golfball 10 not yet having the roughness (ruggedness) produced on thesurface of the coating layer 4 is placed on the support members 22. Inthis state, the rotary body 21 rotates, and meantime, the air gun 23sprays the fine particles over the golf ball 10 while suitably moving.The fine particles can be thereby sprayed over the entire surface of thecoating layer 4.

Herein, when a pressure for spraying the fine particles is by far lowerthan the general standard, a possibility is that the desired roughnesson the surface of the coating layer 4 cannot be acquired. Whereas whenthe pressure for spraying the fine particles is by far higher than thegeneral standard, the fine particles break through the coating layer 4and conceivably cause a damage to the cover 3. From this point of view,the pressure for spraying the fine particles is preferably 1 to 10 bar.

The fine particles used by this method may be properly selectedcorresponding to the embodiment. For instance, the fine particles to besprayed over the coating layer 4 may involve using natural ores,synthetic resins, ceramic particles and other equivalent particles. Theusable natural ores are, e.g., SiC, SiO₂, AL₂O₃, MgO and Na₂O, ormixtures thereof are also usable. For instance, the usable syntheticresins are thermoplastic resins or thermosetting resins each containinga melamine resin or another equivalent resin as a main component, ormixtures thereof are also usable. The usable ceramic particles are metaloxides instanced by zirconia and other equivalent oxides.

However, an average particle size of the fine particles to be sprayed ispreferably equal to or larger than 50 μm in order to acquire the desiredroughness on the surface of the coating layer 4. When the averageparticle size of the fine particles to be sprayed is smaller than 50 μm,the desired roughness on the surface of the coating layer 4 is notacquired, resulting in a possibility of being unable to give a desiredaerodynamic effect to the golf ball 10. On the other hand, though anupper limit of the average particle size of the fine particles is notparticularly restricted, the fine particles probably become hard to besprayed when the particle size increases. Hence, the average particlesize of the fine particles is preferably equal to or smaller than 500μm.

Note that the apparatus to spray the fine particles over the coatinglayer 4 may not be limited to such an instance but is properlyselectable corresponding to the embodiment. In the case of producing theroughness over the surface of the coating layer 4 by thus spraying thefine particles, when the thickness of the coating layer 4 is by farsmaller than the general standard, the coating layer 4 is probablyexfoliated upon spraying the fine particles. From this point of view, asdescribed above, it is preferable that the thickness of the coatinglayer 4 is equal to or larger than 5.0 μm. The present method enablesthe desired roughness to be produced on the surface of the coating layer4 by appropriately adjusting the average particle size of the fineparticles, the spraying pressure, the spraying time and other equivalentvalues.

<Roughness Produced by Pressurizing Process>

Further, the roughness can be formed on the surface of the coating layer4 by performing a pressurizing process without depending on the sprayingof the fine particles. For instance, after forming the coating layer 4in the manufacturing process, the golf ball 10 is put into the mold withthe roughness being produced over an internal wall surface of thecavity, and the mold is subjected to the pressurizing process. Theinternal wall surface of the cavity is formed with the protrudedportions and other equivalent portions for producing the desiredroughness, and the desired roughness can be thereby produced on thesurface of the coating layer 4.

The mold used in this process is not particularly limited as long asincluding the portions for producing the roughness, and, however, it isfeasible to use the same mold as the mold employed for molding, e.g.,the dimples 5. The roughness can be produced on the internal wallsurface of the cavity by spraying the fine particles similarly to theforegoing method.

Note that the desired roughness on the surface of the coating layer 4 isnot possibly acquired when the thickness of the coating layer 4 is byfar smaller than the general standard in the case of producing theroughness by this method. From this point of view, as described above,the thickness of the coating layer 4 is preferably equal to or largerthan 5.0 μm.

According to one aspect, the present embodiment aims at providing thegolf ball exhibiting the excellent flying performance owing to themultiplier effect of the depth of the dimple and the roughness on thesurface of the coating layer. As described above, the present embodimentenables the provision of the golf ball exhibiting the excellent flyingperformance owing to the multiplier effect of the depth of the dimpleand the roughness on the surface of the coating layer.

§3 Modified Example

The in-depth description of the embodiment of the present invention hasbeen made so far but is merely an exemplification of the presentinvention in every respect. It is a matter of course that a variety ofimprovements and modifications may be made without deviating from thescope of the present invention. For example, as discussed above, thecore 1, the layer configuration including the intermediate layer 2 andthe cover 3 is not limited to a specific number of layers, and it may besufficient that the coating layer is coated over the surface of at leastthe outermost layer, i.e., the cover member. Note that, to give oneinstance, the golf ball 10 is configured based on a 3-piece structureincluding the core 1, the intermediate layer 2 and the cover 3 in theembodiment discussed above, and the golf ball may, however, beconfigured based on a 2-piece structure including the core and thecover.

WORKING EXAMPLES

Examples of the present invention will hereinafter be described. Thepresent invention is not, however, limited to the Examples that follow.

[Manufacture of Golf Ball]

As demonstrated in following Table 1, 32 types of golf balls accordingto Example 1-18 and Comparative Example 1-14 were manufactured. The golfball according to each of the respective Examples and ComparativeExamples has substantially the same configuration as that of the golfball 10 according to the embodiment described above. Full descriptionswill hereinafter be made.

TABLE 1 Comparative Comparative Comparative Comparative ComparativeComparative Type of Golf Ball Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Dimple Type D1 D2 D3 D4 D5 D1 Fa (mm) 0.218 0.2280.238 0.248 0.258 0.218 Ra (μm) 0.25  0.25  0.25  0.25  0.25  0.43 Comparative Comparative Type of Golf Ball Example 7 Example 8 Example 1Example 2 Example 3 Example 4 Dimple Type D2 D3 D4 D5 D2 D3 Fa (mm)0.228 0.238 0.248 0.258 0.228 0.238 Ra (μm) 0.43  0.43  0.43  0.43 0.54  0.54  Type of Golf Ball Example 5 Example 6 Example 7 Example 8Example 9 Example 10 Dimple Type D6 D4 D3 D5 D2 D1 Fa (mm) 0.268 0.2480.238 0.258 0.228 0.218 Ra (μm) 0.54  0.68  0.81  0.81  0.94  1.07  Typeof Golf Ball Example 11 Example 12 Example 13 Example 14 Example 15Example 16 Dimple Type D6 D3 D4 D2 D3 D4 Fa (mm) 0.268 0.238 0.248 0.2280.238 0.248 Ra (μm) 1.07  1.20  1.20  1.33  1.33  1.33  ComparativeComparative Comparative Comparative Comparative Type of Golf BallExample 17 Example 9 Example 10 Example 11 Example 12 Example 13 DimpleType D1 D2 D3 D4 D5 D6 Fa (mm) 0.218 0.228 0.238 0.248 0.258 0.268 Ra(μm) 1.47  1.47  1.47  1.47  1.47  0.25  Comparative Type of Golf BallExample 14 Example 18 Dimple Type D6 D5 Fa (mm) 0.268 0.258 Ra (μm)1.47  1.33 

(1) Manufacture of Core

In the respective Examples and Comparative Examples, highcis-polybutadiene (manufactured by JSR Corp., product name: BR-730) of100 pts. mass, zinc acrylate of 35 pts. mass, zinc oxide of 5 pts. mass,barium sulfate of 5 pts. mass, diphenyl disulfide of 0.5 pts. mass,dicumyl peroxide of 0.9 pts. mass, and zinc octoate of 2.0 pts. masswere kneaded, whereby a rubber composition for the core was obtained.The rubber composition was put into the mold having a semi-sphericalcavity and constructed from an upper mold and a lower mold and washeated at 170° C. for 18 min, with the result that a core having adiameter of 39.7 mm was acquired.

(2) Molding of Intermediate Layer

Subsequently, in the respective Examples and Comparative Examples, anionomer resin (made by Du Pont Corp., product name: Surlyn 8945) of 50pts. mass, another ionomer resin (Du Pont-Mitsui Polychemical Co., Ltd.,product name: Himilan AM7329) of 50 pts. mass, titanium dioxide of 4pts. mass, and ultramarine blue of 0.04 pts. mass were kneaded by a twinscrew kneading extruder, whereby a resin composition for theintermediate layer was acquired. Then, in the respective Examples andComparative Examples, the intermediate layer was formed by coating theresin composition over the periphery of each core by an injectionmolding method. A thickness of the intermediate layer was 1.0 mm.

(3) Molding of Reinforcing Layer

Next, in the respective Examples and Comparative Examples, a coatingcomposition (Shinto Paint Co., Ltd., product name: Polyn 750LE) with thetwo-part curing type epoxy resin serving as base polymer was prepared. Amain agent liquid of the coating composition is composed to include abisphenol type-A solid epoxy resin of 30 pts. mass and a solvent of 70pts. mass. A curing agent liquid of the coating composition isconstructed to include denatured polyamidoamine of 40 pts. mass, thesolvent of 55 pts. mass and titanium oxide of 5 pts. mass. A mass ratioof the main agent liquid and the curing agent liquid is 1/1. Areinforcing layer was acquired by spraying the coat composition over thesurface of the intermediate layer by a spray gun and retaining the coatcomposition for 6 hours under an atmosphere of 23° C. A thickness of thereinforcing layer was 10 μm.

(4) Molding of Cover

Next, in the respective Examples and Comparative Examples, a resincomposition for the cover was acquired by kneading thermoplasticpolyurethane elastomer (made by BASF Japan Corp., product name:Elastollan XNY85) of 100 pts. mass and titanium dioxide of 4 pts. massby the twin screw kneading extruder. Then, in the respective Examplesand Comparative Examples, half shells were acquired from these resincompositions by a compression molding method. Note that the compressionmolding for the half shell was conducted under a condition that amolding temperature was 170° C., molding time was 5 min, and a moldingpressure was 2.94 MPa.

A sphere configured to include the core, the intermediate layer and thereinforcing layer was coated with the two half shells. Further, the twohalf shells and the sphere were put into a final mold constructed of theupper mold and the lower mold each having a semi-spherical cavity with acavity surface being provided with a multiplicity of pimples, and acover having the plurality of dimples was acquired by the compressionmolding method. Note that the compression molding of the cover wasperformed under a condition that the molding temperature was 145° C.,the molding time was 2 min, and the molding pressure was 9.8 MPa. Athickness of the cover was 0.5 mm in each the Examples and ComparativeExamples.

Herein, in the respective Examples and Comparative Examples, the dimplesdepicted in FIGS. 3 and 4 were formed. However, in the respectiveExamples and Comparative Examples, as given below, the average value Fa(mm) of the maximum depths was adjusted by controlling the maximum depthDp of the dimple. Specifically, the dimple of Type D1 illustrated infollowing Table 2 was formed in Examples 10, 17 and Comparative Examples1, 6, respectively. Therefore, in the golf ball having the dimple ofType D1, the average value Fa (mm) of the maximum depths of the dimpleswas 0.218 mm.

In Examples 3, 9, 14 and comparative Examples 2, 7, 9, respectively, thedimple of Type D2 illustrated in following Table 2 was formed. Hence, inthe golf ball having the dimple of Type D2, the average value Fa (mm) ofthe maximum depths of the dimples became 0.228 mm.

In Examples 4, 7, 12, 15 and comparative Examples 3, 8, 10,respectively, the dimple of Type D3 illustrated in following Table 2 wasformed. Accordingly, in the golf ball having the dimple of Type D3, theaverage value Fa (mm) of the maximum depths of the dimples became 0.238mm.

In Examples 1, 6, 13, 16 and comparative Examples 4, 11, respectively,the dimple of Type D4 illustrated in following Table 2 was formed.Accordingly, in the golf ball having the dimple of Type D4, the averagevalue Fa (mm) of the maximum depths of the dimples became 0.248 mm.

In Examples 2, 8, 18 and comparative Examples 5, 12, respectively, thedimple of Type D5 illustrated in following Table 2 was formed.Consequently, in the golf ball having the dimple of Type D5, the averagevalue Fa (mm) of the maximum depths of the dimples became 0.258 mm.

In Examples 5, 11 and comparative Examples 13, 14, respectively, thedimple of Type D6 illustrated in following Table 2 was formed. Hence, inthe golf ball having the dimple of Type D6, the average value Fa (mm) ofthe maximum depths of the dimples became 0.268 mm.

TABLE 2 Curv- Diameter Maximum ature Total Dm Depth Dp CR Volume VolumeType Number (mm) (mm) (mm) (mm³) (mm³) D1 A 72 4.60 0.244 22.1 2.03146.3 B 54 4.50 0.229 23.1 1.82 98.4 C 30 4.30 0.219 21.1 1.59 47.6 D 544.20 0.214 20.1 1.48 79.9 E 108 4.00 0.204 18.2 1.28 138.5 F 12 2.900.149 10.6 0.49 5.9 Total 330 — — — — 516.6 D2 A 72 4.60 0.254 20.4 2.11152.3 B 54 4.50 0.239 21.2 1.90 102.7 C 30 4.30 0.229 19.3 1.66 49.8 D54 4.20 0.224 18.4 1.55 83.7 E 108 4.00 0.214 16.7 1.35 145.3 F 12 2.900.159  9.6 0.53 6.3 Total 330 — — — — 540.1 D3 A 72 4.60 0.264 19.0 2.20158.3 B 54 4.50 0.249 19.5 1.98 107.0 C 30 4.30 0.239 17.8 1.73 52.0 D54 4.20 0.234 17.0 1.62 87.4 E 108 4.00 0.224 15.4 1.41 152.1 F 12 2.900.169  8.8 0.56 6.7 Total 330 — — — — 563.5 D4 A 72 4.60 0.274 17.7 2.28164.3 B 54 4.50 0.259 18.2 2.06 111.3 C 30 4.30 0.249 16.6 1.81 54.2 D54 4.20 0.244 15.8 1.69 91.2 E 108 4.00 0.234 14.4 1.47 158.9 F 12 2.900.179  8.2 0.59 7.1 Total 330 — — — — 587.0 D5 A 72 4.60 0.284 16.6 2.37170.3 B 54 4.50 0.269 17.0 2.14 115.6 C 30 4.30 0.259 15.5 1.88 56.4 D54 4.20 0.254 14.8 1.76 95.0 E 108 4.00 0.244 13.4 1.53 165.7 F 12 2.900.189  7.6 0.63 7.5 Total 330 — — — — 610.5 D6 A 72 4.60 0.294 15.6 2.45176.3 B 54 4.50 0.279 15.9 2.22 119.9 C 30 4.30 0.269 14.5 1.95 58.6 D54 4.20 0.264 13.9 1.83 98.7 E 108 4.00 0.254 12.6 1.60 172.6 F 12 2.900.199  7.1 0.66 7.9 Total 330 — — — — 634.0Note that FIG. 6 is a graph depicting a relation between an averagemaximum height Fa of the dimples and the arithmetic average roughness Raof the coating layer of the golf ball according to the respectiveExamples and Comparative Examples. Herein, in FIG. 6, Examples 1-18 werenotated by E1-E18, while Comparative Examples 1-14 were notated byC1-C14, respectively.

(5) Formation of Coating Layer

Next, in the respective Examples and Comparative Examples, a coatingmaterial was prepared by blending polyol and polyisocyanate given infollowing Table 3. Note that the coating material was prepared by usinga mixed solvent of toluene and MEK (methyl ethyl ketone) as a main agentso that a concentration of the polyol component becomes 30% by mass. Thecuring agent was prepared by using a mixed solvent of MEK, n-Butylacetate and toluene as solvents so that the concentration of thepolyisocyanate becomes 60% by mass.

TABLE 3 Name of Material Blending Ratio Curing HDI burette denaturedbody/ 40/20 Agent HDI isocyanurate denatured body ※1) IPDI componet 40(IPDI isocyanurate denatured body) Curing Agent/Main Agent (NCO/OH MolarRatio) 0.5/1.0 ※1) Blending of Curing Agent:Mass ratioNote that the following products were used as raw materials forblending.(Main Agent)Polyn #950 made by Shinto Paint Co., Ltd.: hydroxyl value 128 mgKOH/g,urethan polyol containing a polyol component (trimethylol-propane,polyoxy-tetramethylene glycol) and a polyisocyanate component(isophorone diisocyanate).(Curing Agent)(i) An isocyanurate denatured body of hexamethylene-diisocyanate:Duranate TKA-100 (NCO content by percentage: 21.7%) made by Asahi KaseiChemicals Corp.(ii) A burette denatured body of hexamethylene-diisocyanate: Duranate21S-75E (NCO content by percentage: 15.5%) made by Asahi Kasei ChemicalsCorp.(iii) An isocyanurate denatured body of isophorone-diisocyanate:VESTANAT T1890 (NCO content by percentage: 12.0%) made by Degussa Corp.

In the respective Examples and Comparative Examples, the coating layerwas formed by spreading the coating material of each compound over theperiphery of the cover. To be specific, each coating material was spreadwhile moving the air gun being spaced away at a spraying distance (7 cm)from each golf ball in up-and-down directions by rotating the rotarybody on which each golf ball was placed at 300 rpm. An interval, atwhich several layers of coat were applied each time, was set to 1.0 sec.A spraying condition of the air gun was set such that a spraying airpressure was 0.15 MPa, a pumping tank air pressure was 0.10 MPa, aperiod of single-coating time was 1 sec, an atmospheric temperature waswithin a range of 20° C.-27° C., and an atmospheric humidity was equalto or smaller than 65%. Thereafter, the coating material was dried at40° C. in an oven for 24 hours. In the respective Examples andComparative Examples, the coating layer having a thickness of 20 μm wasthereby formed. As a result, in the respective Examples and ComparativeExamples, the golf ball with the diameter being approximately 42.7 mmand the mass being approximately 45.6 g was acquired.

Note that a compressed deformation quantity of the golf ball wasmeasured in the respective Examples and Comparative Examples. Thecompressed deformation quantity was approximately 2.45 mm when a loadwas set to 98N-1274N in the respective Examples and ComparativeExamples.

(6) Production of Roughness on Surface of Coating Layer

Finally, in the respective Examples and Comparative Examples exclusiveof Comparative Examples 1 to 5 and 13, the roughness was produced on thecoating layer of the golf ball by the following method. To be specific,after forming the coating layer, the fine particles were sprayed by theair gun having a nozzle diameter of 8 mm. Ceramic particles containingzirconia as a main component and having a particle size of 75 μm to 250μm were used as the fine particles. At that time, the golf balls wereput by twenties into predetermined processing equipment, and the desiredroughness was produced on the coating layer of each golf ball byappropriately controlling the pressure, the time and the particle sizeof the fine particle while rotating the equipment. In ComparativeExamples 1 to 5 and 13, this process was omitted. The roughness of thecoating layer of each golf ball was as given in Table 1.

Note that the arithmetic average roughness Ra (μm) was measured by usinga surface roughness/contour shape measurement machine (made by TokyoSeimitsu Co., Ltd., product name: Surfcom130A). In the respectiveExamples and Comparative Examples, the golf balls were prepared bysixes, and roughness values were measured at six points within anarbitrary dimple of each golf ball, and an average value of thoseroughness values was set as the arithmetic average roughness Ra (μm) ofthat golf ball.

[Measurement Method]

(1) Compressed Deformation Quantity of Core

A deformation quantity (a quantity of how much the golf ball or the coreshrunk in a compression direction) in the compression direction tillwhen a final load 1275N was applied from a state of applying an initialload 98N to the core was measured as the compressed deformation quantityof the core.

(2) 10% Modulus of Coating Layer

A coating film was prepared by drying and curing the coating material,acquired by blending the main agent and the curing agent, of the coatinglayer at 40° C. for 4 hours. Pursuant to JIS-K7161, a test piece wasprepared by punching out the coating film in a dumbbell shape (gaugelength: 20 mm, width of parallel portion: 10 mm), physical properties ofthe coating layer were measure by use of a peel strength testmeasurement apparatus made by Shimadzu Corp., and a modulus (tensilemodulus of elasticity) when stretched at 10% was calculated.

Film thickness of test piece: 0.05 mm

Tension speed: 50 mm/min

Measurement Temperature: 23° C.

[Carry Test]

Performed was a carry test given below for the thus-manufacture golfball in the respective Examples and Comparative Examples. At first, adriver club (made by Dunlop Sports Co., Ltd., product name: SRIXON Z-TX,shaft hardness: X, loft angle: 8.5 degrees) equipped with a headcomposed of a titanium alloy was mounted in a swing machine of GolfLaboratories, Inc. Next, the swing machine was adjusted so that a headspeed was 50 m/s, a hitting angle (launch angle) was approximately 10degrees, and a spin quantity was approximately 2500 rpm. The swingmachine hit the golf balls by twenties in the respective Examples andComparative Examples, in which case distances from launching points tostatic points were measured, and an average value was examined. Notethat a wind direction was substantially windless when performing thetest. Following Table 4 shows results of the carry test.

TABLE 4 Comparative Comparative Comparative Comparative ComparativeComparative Type of Golf Ball Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Carry (m) 261.1 262.0 263.5 263.0 262.4 261.7 CarryDifference (m) −2.4 −1.5 0.0 −0.5 −1.1 −1.8 Comparative Comparative Typeof Golf Ball Example 7 Example 8 Example 1 Example 2 Example 3 Example 4Carry (m) 263.0 264.1 264.6 264.5 264.5 265.5 Carry Difference (m) −0.50.6 1.1 1.0 1.0 2.0 Type of Golf Ball Example 5 Example 6 Example 7Example 8 Example 9 Example 10 Carry (m) 264.7 265.6 266.2 264.8 265.5265.0 Carry Difference (m) 1.2 2.1 2.7 1.3 2.0 1.5 Type of Golf BallExample 11 Example 12 Example 13 Example 14 Example 15 Example 16 Carry(m) 264.6 265.3 264.7 264.8 264.6 264.5 Carry Difference (m) 1.1 1.8 1.21.3 1.1 1.0 Comparative Comparative Comparative Comparative ComparativeType of Golf Ball Example 17 Example 9 Example 10 Example 11 Example 12Example 13 Carry (m) 264.6 264.3 264.1 264.0 263.8 262.0 CarryDifference (m) 1.1 0.8 0.6 0.5 0.3 −1.5 Comparative Type of Golf BallExample 14 Example 18 Carry (m) 263.6 264.5 Carry Difference (m) 0.1 1.0Note that [Carry Difference (m)] in Table 4 connotes a difference of thecarry from Comparative Example 3.

[Evaluation]

As demonstrated in Table 4, the carry in each Example was longer than ineach Comparative Example. Particularly, the carry in each Example waslonger by 1 or more yards than in Comparative Example 3. In comparisonsbetween Example 17 and Comparative Examples 9-12, the carry decreased asthe average value Fa (mm) of the maximum depths of the dimplesincreased. On the other hand, in comparisons between Examples 1, 2 andComparative Examples 6-8, the carry was basically extended owing to theincrease in average value Fa (mm) of the maximum depths of the dimples.Further, when comparing the Examples (4, 7, 12 and 15) and theComparative Examples (3, 8 and 10) having the same type of dimples witheach other, it was recognized that the carry was not extended simply byincreasing the degree of roughness on the surface of the coating layer.To be specific, it was recognized that the carry initially had anincreasing tendency as the degree of roughness on the surface of thecoating layer was increased but thereafter had a decreasing tendency. Itwas presumed from these recognitions that such a correlation between thedepth of the dimple and the roughness on the surface of the coatinglayer as to enable enhancement of the carry performance of the golfball, could be specified by the relational expression given in theMathematical Expression 1.

The invention claimed is:
 1. A golf ball comprising: a spherical core;one or more cover members to cover the core; and a coating layer to coata cover member configuring an outermost layer of the one or more covermembers, wherein: a plurality of dimples being formed in the covermember of the outermost layer, roughness being produced on a surface ofthe coating layer after applying a coat over the cover member of theoutermost layer, and an average value Fa (mm) of maximum depths of theplurality of dimples and arithmetic average roughness Ra (μm) on thesurface of the coating layer, satisfy a relational expression:−1.5×Fa+0.8≦Ra≦−1.5×Fa+1.8, wherein the arithmetic average roughness Rais equal to or larger than 0.6 μm and equal to or smaller than 0.9 μm,and the average value Fa is equal to or larger than 0.22 mm and equal toor smaller than 0.31 mm.
 2. The golf ball according to claim 1, whereinthe roughness on the surface of the coating layer is acquired by asurface treatment of spraying fine particles over the surface.
 3. Amethod for manufacturing a golf ball, comprising: a step of forming aspherical core; a step of covering the core with one or more covermembers, and forming a plurality of dimples in a cover memberconfiguring an outermost layer of the one or more cover members; a stepof coating the cover member of the outermost layer with a coating layer;and a step of producing roughness on a surface of the coating layer,wherein an average value Fa (mm) of maximum depths of the plurality ofdimples to be formed and arithmetic average roughness Ra (μm) on thesurface of the coating layer, satisfy a relational expression:−1.5×Fa+0.8≦Ra≦−1.5×Fa+1.8, wherein the arithmetic average roughness Rais equal to or larger than 0.6 μm and equal to or smaller than 0.9 μm,and the average value Fa is equal to or larger than 0.22 mm and equal toor smaller than 0.31 mm.